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So, I learned in class that current is defined as positive charges moving from south to north. However, in all reality, the negative charges are moving, but the convention of positive to negative wors so we don't change it. at the same time, electron flow is electrons(negative charges) moving. If current is ACTUALLY electrons moving, then how does is it different from electron flow?

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The following definition of electric current comes from the NCEE reference manual for the PE FE exam in Electrical and Computer Engineering:

"Electric current $i(t)$ through a surface is defined as the rate of charge transport through that surface or

$$i(t)=\frac{dq(t)}{dt}$$

which is a function of time $t$ since $q(t)$ denotes instantaneous charge."

Note that the definition simply says "charge", and there is no mention of whether it is negative or positive charge. The transport of either through a surface meets the definition of current.

However in electrical engineering the convention, as you already know, is to view current as the flow of positive charge. As I understand it (and there is some debate here), the convention is more an historical one as opposed to a technical one and dates back to Ben Franklin's early work with electrostatics.

Bottom line, the convention could just as well have been the flow of negative charge. It doesn't matter as long as one is consistent. Choosing a convention allows us all to talk in the same terms, such as what is meant by "high" vs "low" electrical potential.

Hope this helps.

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  • $\begingroup$ If we have a voltage difference and also both positive and negative charges can move then they will move in opposite directions. Does the direction matters in that derivative? Because if we have a flow we must consider what we consider as a positive and a negative flow. $\endgroup$ Sep 10 '20 at 12:12
  • $\begingroup$ @AntoniosSarikas The direction of current flow doesn't matter in the derivative. It's just the amount of charge passing a point per unit time. It doesn't matter what kind of charge it is. $\endgroup$
    – Bob D
    Sep 10 '20 at 13:58
  • $\begingroup$ When we want to find current don't we integrate current density, that is: $$I=\int \vec{j} \cdot d\vec{A}$$ Now according to what direction we consider positive or negative we get a positive or a negative flow rate. Also if positive charges could move in opposite directions (hypothetically) the flow rate would be zero because the same amount of charges will go in opposite directions in same amount of time. $\endgroup$ Sep 10 '20 at 14:03
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    $\begingroup$ @AntoniosSarikas Which way current flows has no practical effect on what it does. Current is simply the flow of electric charge past a point. While in metals those charge carriers are electrons, in other cases such as electrolytes the charge carriers may be positive ions. In an ionized gas (plasma) both positive ions and electrons may be charge carriers. Since in reality charge carriers can be either positive or negative, no single convention would fit all cases. $\endgroup$
    – Bob D
    Sep 10 '20 at 14:21
  • $\begingroup$ Since, in most cases, the flow of charge is electrons it is generally agreed the selection of the convention that current is the flow of positive charge was a poor one. It goes back to the time of Benjamin Franklin when electricity was still poorly understood. But unless it is changed, I guess we’re stuck with it. We just need to be consistent, and I will leave it at that. $\endgroup$
    – Bob D
    Sep 10 '20 at 14:21
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Current doesn't refer to any specific direction, neither does it require the flow of electrons (any charge carrier will do).

Current is defined as the rate at which positive charge flows through a point ($i=\lim_{\Delta t \to 0}\frac{\Delta q}{\Delta t}$). If your current is generated by the flow of negative charges, we simply consider an equal and opposite flow of positive charge. Thus, when electrons move from S $\to$ N in a wire, we say a current flows from the N $\to$ S direction, and vice-versa.

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in all reality, the negative charges are moving

That really depends on your type of circuit. A few examples:

  • The charge-carriers in metallic circuits (the usual circuits and wiring) are electrons, yes.
  • The charge-carriers in p-type semiconductors (in solar panels, thermoelectric modules, transistors) are positive so-called holes.
  • Charge-carriers in liquids and solid-state diffusion materials and similar (in batteries, fuel cell membranes) are ions of any kind, so can both be positive or negative depending on the scenario.
  • Charge-carriers in plasma (in fusion power plants, lightning, electric arc lighters) can be a mix of released particles, including both protons and electrons. Etc.

If current is ACTUALLY electrons moving, then how does is it different from electron flow

All the above types of charge-carriers can be present in parts of a circuits. It wouldn't make much sense to specifically talk about electron flow because it simply isn't always electrons that are moving.

We therefor stick with the word current, which covers any type of moving charge. But how can the word current cover all moving charge of any type at the same time? How come we don't have to refer to each specific type of moving charge-carrier individually?

Because it turns out that in most relevant situations, anything with a charge behaves more or less the same. The effect we get from electrons moving one way is equivalent to the effect from positive charges moving the other way. At the macroscale we can rarely detect the difference. And so, people back in time have simply decided to talk about everything as was it a positive charge moving. It makes no difference.

It only makes a difference at the microscale, when we want to consider charge-carrier mobility, diffusivity and the like or when a specific type of charge is required such as in the construction of a semiconductor n-type/p-type pair for a solar cell. But in most scenarios and in most electronics, this is not relevant. So, we just talk as if it all was positive charge moving, even when it isn't. That's the convention.

This convention also applies for other proporties, such electric field directions, voltage notation etc.

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This link may help:

Since electric charge is quantized in discrete multiples of the electron charge, it is instructive to look at electric current as the movement of multiple microscopic charge carriers with a drift velocity in a conductor.

current

If current is ACTUALLY electrons moving, then how does is it different from electron flow?

Using the calculator in the link:

drift

The drift velocity of the electrons is low. The transport of energy though of the collective motion, is due to one electron pushing with the electromagnetic interaction the neighbor. This energy goes close to the velocity of light. So the collective effect, the current, is different than the individual electrons' motion, in this example of a current in a conductor.

There are different forms of charge carriers as explained in the other answers.

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